The Chitons. Ill 



MULTIVALVES. 



We have insensibly passed from the Bivalve shells 

 to those composed of several pieces, and therefore 

 called Multivalves ; probably, perhaps, the Kock- 

 borers, last described, come into this division, for 

 although their covering consists mainly of two 

 principal portions or valves, yet there are often 

 additional parts ; in some a calcareous tube enve- 

 lops the whole mollusk, leaving only an opening 

 behind. This is more especially the case with those 

 which most resemble worms, such as the genera 

 Teredina and Teredo, included by Lamarck in the 

 family which he calls Tubulidce. 



The first group of multivalves we shall have to 

 notice, are 



THE CHITONS, 



forming the family Chitonidce. The term has a 

 Greek derivation, and means a coat of mail. These 

 mollusks are covered by a shell formed of eight 

 distinct portions, arranged along the back in a 

 single row, and attached to a mantle which re- 



